Hello Salvatore,
Initial Load program for Org and Employee would get the triggered data into C4C and create them in C4C passing through the Staging area were you can make the changes into the replicated data before loading it into C4C.
Such data brought in via replication need no manual ID mapping, it is maintained automatically. (Which you can confirm in ID mapping for Integration).
Finally if there is any changes done on the On Prem side, we can trigger delta load using same Initial load program with Delta Load option for this object.
Regards,
Chandan